This invention relates to a method of cleaning the cooling system of an internal engine and more specifically to a method of cleaning the cooling system of a diesel engine for both on-road and off-road vehicles.
Diesel engines for vehicles typically operate at high temperatures. At these elevated temperatures, unstable silicates and phosphates in the anti-freeze (typically an alcohol, usually an aqueous ethylene glycol solution with various additives) combine with the hard water and corrosion products in the cooling system to form a gel. This gel may consist of calcium silicates, calcium phosphates, and magnesium silicate. The gel will eventually restrict the flow of coolant through the cooling system and result in an inability to properly cool the engine or heat the cab of a car or truck. It will also cause hot spots within the engine. Both the overall overheating and the localized heating lead to such problems as increased oil temperatures, premature water pump failure, scuffed cylinder liners, and cracked or warped heads. The engines are also subject to the build-up of scale, rust, corrosion products, and the like, which not only cause their own problems such as sticking thermostats and failed water pump seals, but interact physically and chemically with each other and the gel to exacerbate the problems.
Presently, to effectively clean a diesel cooling system, the system must be treated by draining and flushing the engine to remove loose contaminants, then mixing and adding a liquid cleaning agent, running it through the engine for three to four weeks, then draining and flushing the cooling system to remove the loosened particles and then filling it again with coolant. Such cleaning liquids include products sold under the trademark Restore, which is manufactured by Fleetguard, Inc., and Nalprep 2001, which is manufactured by Nalco Chemical Company. These products must be diluted before they are added to the system, to prevent localized damage to the system. Such a method of cleaning is both complicated and expensive, in that it requires considerable labor and requires substantial vehicle downtime Therefore, it is not uncommon for diesel engine cooling systems to go for long periods without cleaning. It has been estimated that more than half of all diesel engine failures are directly attributable to cooling system problems.
Formulations for cooling system cleaners are widely known. The best cleaners for general purpose cleaning are known as inhibited alkaline chelant cleaners; both Nalco's Nalprep 2001 and Fleetguard's Restore are of this type. They include a chelating agent, such as a polycarboxylic acid salt of an amine (for example, an alkaline salt of nitrilotriacetic acid or, preferably, one of the alkaline salts of ethylenediaminetetraacetic acid (EDTA)), one or more corrosion inhibitors to prevent the cleaned surfaces from immediately corroding again, and a buffer to maintain an alkaline pH. The patent literature describes a number of such cleaners, including U.S. Pat. Nos. 2,802,788 (Flaxman), 3,962,109 (Oberhofer et al), 4,279,768 (Busch), and 4,540,443 (Barber).
Once the cooling system has been cleaned, it must immediately be protected against further corrosion and contamination by the addition of a chemical inhibitor mixture. These inhibitors, however, do not dissolve corrosion products or gel which have already formed. Thus, adding such chemical inhibitors to a dirty or corroded cooling system may do further damage to the system, as by causing scale or corrosion to break off in chunks. Such inhibitor mixtures generally include compounds for inhibiting corrosion of the materials encountered by the coolant, such as ferrous metals, aluminum, and red metals such as brass, bronze and copper, as well as such additional chemicals as defoamers, surfactants, pH controllers, and indicators. Generally, such inhibitor mixtures include chemicals (alkaline buffers) to maintain the pH of the coolant above 7. Examples of such inhibitor mixtures are well known, and are described, for example in U.S. Pat. Nos. 3,147,223 (Boies et al), 3,948,792 (Watson et al), 4,242,214 (Lambert), 4,404,113 (Peters et al), 4,587,028 (Darden), 4,707,286 (Carr), 4,711,735 (Gulley), 4,717,495 (Hercamp et al), and 4,744,949 (Hoots et al).
The cooling system of a typical diesel engine differs from that of other typical internal combustion engines in that it includes a filter for removing loose debris from the circulating coolant. The coolant filter is a by-pass filter, which typically sees all of the coolant in the system over a period of about sixteen to twenty cycles of the water through the system.
Rather than add inhibitor mixtures to the coolant system directly as concentrated solutions, they are frequently added to the system by enclosing them in the coolant filter A commercially available filter of this type is sold by Nalco Chemical Company as its Nalcool 3000 cooling system filter. A recently introduced version of this filter, sold under the trademark Nalcool Need-Release and described in bulletin TT-108, includes membranes which release a solid pelletized inhibitor as needed over a period of up to one year or 100,000 miles. The patent literature also describes such filters containing an inhibitor package. Examples are U.S. Pat. Nos. 3,348,693 (Cornell), 3,645,402 (Alexander et al), and 4,842,731 (Dobrez et al). As previously noted, the use of such filter/inhibitor packages with a dirty engine may be worse than adding no inhibitors.